The following publications disclose the techniques relating to an optical scan unit constituted as a single integral body with a function for deflecting a light beam from a light emission source by a deflection unit to repeat scanning. That is,    a) Japanese Patent Application Laid-Open Publication No. 4-96014,    b) Japanese Patent Application Laid-Open Publication No. 4-328715,    c) Japanese Patent Application Laid-Open Publication No. 6-3613,    d) Japanese Patent Application Laid-Open Publication No. 9-146129,    e) Japanese Patent Publication No. 2668725, and    f) Japanese Patent Publication No. 2722630.However, these publications have failed to disclose a concept of making a module of a single integral optical scan unit associated with a standard size paper sheet, nor a mounting unit for mounting to another member.
The following publications disclose the techniques relating to an optical scanner having a plurality of optical scan unit arranged in a direction as a single integral body with a function for deflecting a light beam from a light emission source by a deflection unit to repeat scanning. That is,    g) Japanese Patent Application Laid-Open Publication No. 6-255169,    h) Japanese Patent Application Laid-Open Publication No. 10-68899, and    i) Japanese Patent Application Laid-Open Publication No. 11-95152.However, these publications have failed to disclose a mounting unit for mounting a plurality of optical scan unit to another member. Although an object is proposed to render a joint part of scan lines unobtrusive when a single scan line is divided to be simultaneously scanned with two light beams, it is difficult to grasp as a clear concrete measure for solution.
As a technique to make a joint part of two light beams unobtrusive when a single scan line is divided to be simultaneously scanned with the two light beams, there has been disclosure in Japanese Patent Application Laid-Open Publication No. 11-174355 such that, between an output time of a sensor detection output as a write position detection signal of an image data on a surface to be scanned by a first light beam and an output time of a sensor detection output as a write position detection signal of an image data on a surface to be scanned by a second light beam, a time difference data in terms of a number of faces of a rotary multi-mirror is based on to determine an average, to calculate therefrom a start position of image writing by the second light beam.
Further, the optical scanner has been used since ever as a writing optical system for an electronic photographic image generator such as a digital copier. A conventional electronic photographic image generator using a conventional optical scanner is provided with a photo-sensitive drum which is rotated at a constant speed with a main motor as a drive source. Around the photo-sensitive drum are disposed a charge collotron, the optical scanner, an image developer, a transfer collotron, and a cleaner. The charge collotron has electric charges uniformly charged on a surface of the photo-sensitive drum. The optical scanner irradiate the uniformly charged surface of the photo-sensitive drum with a light beam (laser beam) to form an electrostatic latent image. The image developer gives toner to the electrostatic latent image formed on the surface of the photo-sensitive drum, for image development. The transfer collotron transfers onto a paper sheet a toner image formed on the photo-sensitive drum surface after the image development. The cleaner collects remaining toner on the photo-sensitive drum surface after transfer of the toner image. After cleaning by the cleaner, the photo-sensitive drum surface is again charged by the charge collotron, whereby image formation is can be repeated.
The optical scanner has an optical scan unit (optical scan module) arranged therein. The optical scan unit is made up by an enclosure, and a scanning optical system disposed in the enclosure to perform light-beam generation, modulation, and deflection. A light beam output from the optical scan unit scans a mirror surface of a reflection mirror disposed in the optical scanner. A reflected light beam from the reflection mirror is repeatedly used to scan a surface of a photo-sensitive drum, as described, in parallel to an axial direction of the photo-sensitive drum. The scan direction parallel to the axial direction of the photo-sensitive drum is called a principal scan direction. The direction of movement along the photo-sensitive drum surface is called a subsidiary scan direction. The scanning optical system is constituted with a laser diode, a collimator lens, a first cylinder lens, a polygon mirror, an fθ lens, and a second cylinder lens.
In the electronic photographic image generator having an optical scanner as described, if a vibration of a body of the electronic photographic image generator is transmitted to a scanning optical system of the optical scanner, the scanning optical system of the optical scanner is vibrated, which constitutes a cause of occurrence of a band-like unevenness of image concentration, called banding, to appear in a subsidiary scan direction.
There have been proposed since ever various optical scanners to prevent an unevenness of image concentration due to vibration of a scanning optical system. Among them, an optical scanner described in Japanese Patent Application Laid-Open Publication No. 9-33844 is constituted with a light beam generator for generating a light beam, a light deflector for deflecting the light beam output from the light beam generator, a predetermined vibration-generating component generating a vibration that may have an effect on a path of the light beam, a support plate having a hole portion fitted on a body circumference of the vibration-generating component, a side wall arranged to stand on an edge portion of the support plate, a plurality of ribs configured to be in contact with the support plate and radially disposed from the hole portion toward the side wall at a predetermined level, and an optical box for accommodating at least the light deflector and the vibration-generating component. In this optical scanner, the plurality of ribs configured to be in contact with the support plate and radially disposed from the hole portion toward the side wall at the predetermined level keep the rigidity of the support plate to thereby prevent unevenness of image concentration due to vibration. In conventional optical scanners in which a single scanning optical system is disposed on a support plate, it is possible to prevent unevenness of image concentration due to vibration by keeping the rigidity of the support plate in a described manner.
However, in conventional optical scanners in which a plurality of optical scan modules (optical scan units) are arrayed on a support plate (substrate), as each optical scan module is disposed on or in vicinity of a loop of vibration when the support plate (substrate) vibrates, respective scanning optical systems are vibrated as a whole, with a failure to prevent a degrading of image due to vibration, as a problem.
For example, as shown in FIG. 32, in case an optical scanner has three optical scan modules 1301, 1302, and 1303 arrayed on a substrate 1304 and deflectors (polygon mirrors) of the optical scan modules are disposed on parts a1, b1, and c1 corresponding to loops of a vibration of the substrate 1304 illustrated by a curve 1201, then as shown in FIG. 33, respective scan lines 1305, 1306, and 1307 of the scan modules 1301, 1302, and 1303 are shifted in a subsidiary scan direction, so that joint parts of the scan lines 1305, 1306, and 1307 of the scan modules 1301, 1302, and 1303 are rendered non-connectable, causing a degrading of image, as a problem. The degrading of image due to non-connectable joint parts of the scan lines 1305, 1306, and 1307 of the scan modules 1301, 1302, and 1303 is caused by vibration of the substrate 1304, and appears as a periodical shift in the image to be recognizable by human eyes. Further, also spaces between the scan lines 1305, 1306, and 1307 of the scan modules 1301, 1302, and 1303 are made uneven as shown in FIG. 33, causing uneven concentrations, as a problem.